Electrical signals modulated at Radio Frequencies (RF), for example at or below 50 GHz, are employed to provide high speed telecommunications at high data rates. Discontinuities in electrical conductors conveying RF signals are prone to excite different signal resonance modes, especially in a millimeter waveband.
For example, within current electro-optical (E-O) interfaces between signal modulators and coherent Digital Signal Processing (DSP) chips, Gilbert's Push-On (GPO) and GPPO connectors are employed either edge-mounted or surface-mounted. FIGS. 1A, 1B and 1C show conventional GPO and GPPO connectors mounted on a PCB board to convey signals between E-O Modulators and Coherent DSP chips. Conventional Printed Circuit Board (PCB) connectivity attempts suffer from disadvantages and defects including susceptibility to different signal resonance modes even in the lower frequency band of 10 GHz˜20 GHz.
FIG. 1A illustrates a GPPO connector surface-mounted to a PCB of a signal modulator card. GPPO connector 100, using a bent pin 102, is surface mounted 104 on a PCB pad 106. The bent pin 102 end PCB attachment is surrounded with rectangular array 108 of ground vias. Pin 102 has two bends within connector body 100 for a total of three bends including a bend for the pin 102 leading into a pad of the PCB trace.
FIG. 1B illustrates GPO connectors edge-mounted to a PCB of a signal modulator component card. The PCB needs a rectangle cut-out to fit each connector body 110 on edge. GPO connectors 110 always employ an air gap 114, about 0.5˜3 mils wide, between connector body 110 and the PCB cut-out necessary for component assembly.
FIG. 1C illustrates a conventional GPPO connector employing a similar air gap 114 between connector body and PCB cut-out.
The connector to PCB signal trace transition structures illustrated in FIGS. 1A, 1B and 1C have been found to make it very easy to excite different RF signal resonance modes, especially in the millimeter waveband. Such resonance results in large notches/ripples in insertion loss and return loss, and cause system failure due to the resulting faulty transfer function. Such system performance failures incur huge cost due to product re-spin and deployment delays. This is a common issue recognized in the art particularly in manufacturing coherent DSP line cards and E-O modules.
As an example, FIG. 2A illustrates lab measured resonance notches at 30 GHz when using surface mounted GPPO connectors 100 as illustrated in FIG. 1A.
FIG. 2B illustrates factory measured resonance notches between 16 GHz˜18 GHz when using GPO connectors 110 edge-mounted to a PCB as illustrated in FIG. 1B.
FIG. 2C illustrates measured resonance notches between 16 GHz˜20 GHz when using an edge mounted GPPO connector with an air gap.
The above illustrated resonance notches in the transfer function could not be compensated out with current Finite Impulse Response (FIR) and/or passive equalizers within a coherent DSP chip because they are too sharp. Such electrical interfaces between E-O modulator and DSP chips are a “bandwidth bottleneck” for high speed telecommunications. There is a need to improve RF signal coupling into and out of a signal trace of a PCB via a RF connector.